1. Field of the Invention
The present invention relates to a flame detector for determining presence or absence of flame fluctuation, and more particularly to a flame detector capable of simply and reliably detecting the flame fluctuation.
2. Description of the Related Art
In order to distinguish a flame of fire to be determined from, for example, a high-temperature object except for the flame, which causes a false alarm, various conventional methods for determining the presence or absence of the flame based on flame fluctuation are used.
In a conventional fire detector and a conventional fire detecting method (for example, see JP 2002-162296 A (first page and FIG. 1)), a detection output from a detection sensor for receiving light energy and converting the light energy into an electrical signal is subjected to frequency analysis using a fast Fourier transform method. A pattern of an obtained frequency spectrum distribution is examined and compared with a spectral component of a flame in a center frequency band thereof, a spectral component of a rotating lamp in a frequency band thereof, and a spectral component of another object in a low frequency band thereof. When the spectral pattern of the flame is detected, the occurrence of the fire resulting from the flame is determined.
When the presence or absence of the flame of the fire is to be determined, various conventional methods are used to obtain infrared rays of at least two wavelength bands, of infrared rays emitted from the flame, in relation to a CO2 resonance band or the like and eliminate an infrared ray from a high-temperature object based on a ratio between the obtained infrared rays.
In a conventional infrared ray flame detector (for example, see JP2000-356547 A (first page and FIG. 1)), an infrared ray of a wavelength specific to fire and an infrared ray of a wavelength close thereto are detected. The occurrence or nonoccurrence of the fire resulting from the flame is determined based on a ratio between energy quantities of the detected two infrared rays.
In the conventional fire detector and the conventional fire detecting method, in order to determine the presence or absence of the flame based on flame fluctuation, it is necessary to produce the pattern of the frequency spectrum distribution. In addition, it is necessary to process the detection output from the detection sensor using the fast Fourier transform method and distinguish the detection output from a transient output. Therefore, there is a problem in that processing is complicated to take a time and a trouble and lack the reliability of fire determination.
In the conventional infrared ray flame detector, the infrared ray of the wavelength specific to the fire and the infrared ray of the wavelength close thereto are detected and the occurrence or nonoccurrence of the fire resulting from the flame is determined based on the ratio between the energy quantities of the detected two infrared rays. However, the fluctuation of a ratio between outputs produced by an actual flame is not constant but varies. Therefore, there is a problem in that the occurrence or nonoccurrence of the fire resulting from the flame cannot be reliably detected based on only the fact that an output ratio between the two infrared rays is within a predetermined range.